Hybrid-type stepping motors, for example, are generally structured with a configuration wherein a stator with coils wrapped around a ring-shaped stator stack, which is a pressed stack of thin iron plates, is positioned with a slight gap around a rotor wherein a magnet is attached to a rotor stack which, similarly, is a pressed stack of thin iron plates. In this type of stepping motor, the magnetic polarity of the rotor is attracted to the magnetic polarity of the stator when a current is applied to the coil, causing the rotor to be held in a specific position, where the rotor is rotated in steps by changing the phase of the electric current applied to the coil.
Normally a motor, including the stepping motor described above, has a protective casing that contains the rotor and stator, where a shaft that serves as the output axel and which is attached in the center of the rotor, is held by the casing through a bearing, such as a ball bearing, so as to rotate freely. Well known casing structures include structures wherein there is a single casing formed by bonding into a single unit casing segments wherein the casing was divided along the axial direction of the shaft, and structures wherein the stator stacks of the stators are interposed between the various casing segments so that the stator is secured within the casing when the casing segments are bolted together. (See, for example, Patent Reference 1 and Patent Reference 2.)
The motors disclosed in the publications listed above are complicated in terms of the attachment operations wherein two casing segments are bolted together while the stator is held in a state wherein it is interposed between the two casing segments, and such a motor tends to have an increased number of parts as well. Furthermore, because there is the need for processing by which to fabricate the bolt holes and screw holes for bolting together the various casing segments, there has been a problem in that here has been a large number of manufacturing processes. Furthermore, the metal particles produced when fastening the units by turning the bolt can get into the thin gap between the rotor and the switch, causing problems in rotation. These problems tend to reduce manufacturing efficiency, and thus the development of a technology by which to solve these problems is desirable. Furthermore, in a structure wherein bolts are used to fasten the parts to each other, there has been the danger that the bolts would become lose over long-term operation, tending to lead to rattling and play in the position in which the stator is held.